The low Sr/Ba ratio on some extremely metal-poor stars

Simple item page
dc.contributor.authorSpite, M.
dc.contributor.authorSpite, F.
dc.contributor.authorBonifacio, P.
dc.contributor.authorCaffau, E.
dc.contributor.authorFrancois, P.
dc.contributor.authorSbordone, L.
dc.date.accessioned2025-01-23T21:41:56Z
dc.date.available2025-01-23T21:41:56Z
dc.date.issued2014
dc.description.abstractContext. It has been noted that, in classical extremely metal-poor (EMP) stars, the abundance ratio of two well-observed neutron-capture elements, Sr and Ba, is always higher than [Sr/Ba] = -0.5, which is the value of the solar r-only process; however, a handful of EMP stars have recently been found with a very low Sr/Ba ratio.
dc.description.abstractAims. We try to understand the origin of this anomaly by comparing the abundance pattern of the elements in these stars and in the classical EMP stars.
dc.description.abstractMethods. For a rigorous comparison with previous data, four stars with very low Sr/Ba ratios were observed and analyzed in the same way as in the First Stars program: analysis within LTE approximation through 1D (hydrostatic) model atmosphere, providing homogeneous abundances of nine neutron-capture elements.
dc.description.abstractResults. In CS 22950-173, the only turnoff star of the sample, the Sr/Ba ratio is, in fact, found to be higher than the r-only solar ratio, so the star is discarded. The remaining stars (CS 29493-090, CS 30322-023, HE 305-4520) are cool evolved giants. They do not present a clear carbon enrichment, but in evolved giants C is partly burned into N, and owing to their high N abundance, they could still have initially been carbon-rich EMP stars (CEMP). The abundances of Na to Mg present similar anomalies to those in CEMP stars. The abundance patterns of the neutron-capture elements in the three stars are strikingly similar to a theoretical s-process pattern. This pattern could at first be attributed to pollution by a nearby AGB, but none of the stars presents a clear variation in the radial velocity indicating the presence of a companion. The stellar parameters seem to exclude any internal pollution in a TP-AGB phase for at least two of these stars. The possibility that the stars are early-AGB stars polluted during the core He flash does not seem compatible with the theory.
dc.fuente.origenWOS
dc.identifier.doi10.1051/0004-6361/201423658
dc.identifier.eissn1432-0746
dc.identifier.issn0004-6361
dc.identifier.urihttps://doi.org/10.1051/0004-6361/201423658
dc.identifier.urihttps://repositorio.uc.cl/handle/11534/101650
dc.identifier.wosidWOS:000345282600040
dc.language.isoen
dc.revistaAstronomy & astrophysics
dc.rightsacceso restringido
dc.subjectstars: abundances
dc.subjectstars: Population II
dc.subjectGalaxy: evolution
dc.subjectGalaxy: halo
dc.titleThe low Sr/Ba ratio on some extremely metal-poor stars
dc.typeartículo
dc.volumen571
sipa.indexWOS
sipa.trazabilidadWOS;2025-01-12
Files
Collections
Artículos de revistas